The mammalian midbody is an enigmatic structure in that while it is a constant feature of mitosis and cytokinesis, its exact relationship to these important cellular events is not understood. The proposed work is directed toward answering some of the questions regarding the composition of the midbody and its possible functional roles in cell division. Large populations of post-telophase mitotic cells will be used to isolate the midbodies, and to examine their composition by polyacrylidme gel electrophoresis. Midbody components will be used to prepare antibodies for immunofluorescence to determine distribution of these components prior to late anaphase, when they are first seen by electron microscopy. Midbodies will be freeze fractured to examine the plasma membrane overlying the midbody matrix for differences in particle distribution indicating association between the membrane and the matrix.